1. Field of the Invention
This invention relates to analog interface circuits and more particularly to analog interface systems for use in conjunction with digital signal processors.
2. Description of the Prior Art
To reduce the cost, size, power dissipation and complexity of an analog interface system, it is usually preferable to include all of the circuitry of the system in a minimum number of integrated circuits. In this preferred embodiment, as in such systems as calculators, electronic games and appliance controllers, the entire system is integrated in a single chip.
U.S. Pat. No. 4,638,451--"Microprocessor System with Programmable Interface" issued on Jan. 20, 1987 and assigned to the assignee of this invention involves a microprocessor system that includes an analog input channel and an analog output channel. The analog input channel has an analog to digital converter and the analog output channel has a digital to analog converter. These converters have conversion rates that are selected by an instruction from the CPU. Also, the cut-off points of the filters are selected. The control for the system resides in the CPU. In the preferred embodiment of '451, three separate semiconductor integrated circuits are employed. The digital data converted from the analog input data is stored and then sent in parallel upon request by the CPU. When the digital data has been acted upon by the CPU, it is sent, at the CPU's direction, to the output channel, in parallel.
By contrast, the analog interface circuit of this invention is implemented, in the preferred embodiment, in a single semiconductor integrated circuit. The analog interface system of the present invention directs a signal processor with respect to when the signal processor will receive digital data in a serial stream and when the signal processor will send processed digital data to the output channel in serial fashion.
By relieving the signal processor of its duty to determine when the transmission and reception of data will occur, the present invention enables the signal processor to perform other tasks. Also, by serially transmitting data, the number of pins required is minimized and therefore the number of separate semiconductor integrated circuits is reduced.